System and method for using ultramicroporous carbon for the selective removal of nitrate with capacitive deionization

ABSTRACT

The present disclosure relates to a flow through electrode, capacitive deionization (FTE-CDI) system which is able to adsorb nitrates from water being treated using the system. The system makes use of a pair of electrodes arranged generally parallel to one another, with a water permeable dielectric sandwiched between the electrodes. The electrodes receive a direct current voltage from an electrical circuit. At least one of the electrodes is formed from a carbon material having a hierarchical pore size distribution which includes a first plurality of pores having a width of no more than about 1 nm, and a second plurality of micro-sized pores. The micron-sized pores enable a flow of water to be pushed through the electrodes while the first plurality of pores form adsorption sites for nitrate molecules carried in the water flowing through the electrodes.

STATEMENT OF GOVERNMENT RIGHTS

The United States Government has rights in this invention pursuant toContract No. DE-AC52-07NA27344 between the U.S. Department of Energy andLawrence Livermore National Security, LLC, for the operation of LawrenceLivermore National Laboratory.

FIELD

The present disclosure relates to capacitive desalination systems andmethods, and more particularly to systems and methods for flow throughelectrode, capacitive deionization (FTE-CDI) which incorporate a newelectrode construction for effectively removing nitrate from a mixtureof ions in fluid (water) flowing through the system.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

The current state-of-the-art for water desalination is reverse osmosis(RO). Reverse osmosis uses membranes that allow water, but not salt, topass through the membranes. Pressure is applied to the feed side,pushing water across the membrane to overcome membrane resistance, aswell as the osmotic pressure. Energy use in RO scales with the amount ofwater produced. For seawater, the energy efficiency of RO isunsurpassed, however at low salt concentration the energy efficiency ofRO is significantly reduced. Furthermore, RO membranes arenon-selective, which means that one must remove all ions to remove aparticular contaminant. This further reduces the possible efficiency ofusing RO to treat water for specific trace contaminants.

Capacitive deionization (CDI) is a more recently developed technology.Unlike membrane-based methods, CDI removes salt with electric fields.The charged salt ions are attracted to the charged porous electrodes andthus removed from the water. The device is operated by applying avoltage to the two spaced apart electrodes, which act like plates of asupercapacitor. While water passes through the device, salt ions areattracted to the charged surface and thus removed from the feed water.The energy cost of CDI is proportional to the amount of salt removed,thus giving it the potential to be more energy efficient than RO in lowsalinity regimes. Because CDI is an inherently low-pressure operationand cell and electrode components are made from low-cost materials, thecapital costs are also expected to be significantly less than RO.

Flow-through electrode capacitive deionization (FTE-CDI) is a technologythat involves flowing feed water to be desalinated through the porouselectrodes of a capacitive deionization system, rather than between theelectrodes as in a conventional CDI device. The assignee of the presentapplication is a leader in the development of this technology, as willbe appreciated from the disclosure of U.S. Patent Publication No.2012/0273359 A1, published Nov. 1, 2012, the disclosure of which ishereby incorporated by reference into the present disclosure. In view ofthe known advantages of an FTE-CDI system, significant interest existsin even further enhancing and improving the capabilities of such asystem to even more effectively and efficiently perform desalination onsalt water and/or to remove other types of ions from water.

In addition to general salinity reduction, a particular area of interestin CDI research is the selective removal of specific ionic contaminantsfor increased energy efficiency and to more effectively utilize removalcapacity. One of the major contaminants of interest in present day CDIresearch is nitrate, which is regulated by the US EnvironmentalProtection Agency to a maximum contaminant level in drinking water of 10mg/L (as N) or 0.7 mM as NO₃. The concentration of nitrate ingroundwater is increasing by a reported 1-3 mg/L/yr due to a number offactors including human activities involving agriculture, for examplefrom fertilizer runoff and disposal of municipal effluents by sludgespreading on fields. Other factors contributing to the increasedconcentration of nitrate found in groundwater include atmosphericemissions from energy production sources, as well as combustion enginesof present day motor vehicles. Accordingly, there is a growing interestin developing systems for more effectively removing nitrates, inparticular, from groundwater, making the development of effectivetreatment methods increasingly important.

SUMMARY

In one aspect the present disclosure relates to a flow throughelectrode, capacitive deionization (FTE-CDI) system. The system maycomprise a pair of electrodes arranged generally parallel to oneanother; a water permeable dielectric arranged between the electrodes soas to be sandwiched between the electrodes; and an electronic circuitfor applying a direct current voltage across the electrodes. At leastone of the electrodes may be formed from a carbon material having ahierarchical pore size distribution, the hierarchical pore sizedistribution including a first plurality of nano-sized pores having awidth of no more than about 1 nm, and a second plurality of pores havingmicron-sized pores that enable a flow of water to be pushed through theelectrode. The first plurality of pores form adsorption sites fornitrate molecules carried in the water flowing through the at least oneelectrode.

In another aspect the present disclosure relates to an ultramicroporouselectrode for use in a flow through, capacitive deionization (FTE-CDI)system for adsorbing nitrate molecules contained in water being fed intothe electrode for treatment. The electrode may comprise a carbon aerogelmember having a hierarchical pore size distribution. The hierarchicalpore size distribution may include a first plurality of ultramicroporesrandomly distributed throughout a thickness of the carbon aerogelmember, and each forming a slit having a width of no more than about 1nm; and a second plurality of micron-sized pores randomly distributedthroughout the thickness of the carbon aerogel member. The micron-sizedpores are sufficiently large to enable fluid flow paths to be formedthrough the entire thickness of the carbon aerogel member, which enablea flow of water to be pushed through the thickness of the carbon aerogelmember. The first plurality of pores form adsorption sites for capturingnitrate molecules carried in the water flowing through the carbonaerogel member.

In still another aspect the present disclosure relates to a method formaking a carbon aerogel electrode material. The method may comprisemaking a wet organic sol-gel form; carbonizing the sol-gel form at atemperature of from about 900° C. to about 1000° C., for from about 2 toabout 4 hours; and activating the carbonized sol-gel under carbondioxide flow, for from about 0.5 hours to about 1.5 hours, at from about900° C. to about 1000° C.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a high level block diagram of one embodiment of a FTE-CDIsystem in accordance with the present disclosure for removing nitratefrom a flowing fluid, for example from flowing water through the system

FIG. 1a is a highly simplified enlargement of a portion of one of theelectrodes shown in FIG. 1 illustrating in a highly simplified mannerthe microporous (i.e., nanometer scale) pore structure and the micronsized flow paths formed in each of the electrodes, the microporousstructure being well suited for capturing nitrate contained in a flowingfluid;

FIG. 2 is a simplified high level illustration showing a portion of oneof the electrodes in FIG. 1 to illustrate how the nitrate molecule fitswithin one of the ultramicropores, while a chloride molecule and sulfatemolecule do not fit stably in the ultramicropore;

FIGS. 3a, 3b, 3a 1 and 3 b 1 are illustrations showing the distributionof solvating water molecules around the disc-like nitrate molecule, andwherein FIG. 3a shows the XY (or equatorial) plane of nitrate, which hasstrongly bound water, indicated by red in the plot of FIG. 3a 1, andwherein, FIG. 3b shows the ZX (or axial) plane, which has much weakerinteractions with solvating water, indicated by the lack of red in theplot of FIG. 3b 1, which implies that the overall shape of the solvatednitrate molecule is disc-like;

FIG. 4 is a high level flowchart summarizing various operations that maybe performed in forming the electrodes shown in FIG. 1;

FIGS. 4a and 4b illustrate high and low magnification micrographs,respectively, obtained from a scanning electron microscope showing theelectrodes after carbonization and activation;

FIG. 5 is a graph showing measurements of the micro-pore sizedistribution from N₂ adsorption measurements of the micro-pores formedin a carbon aerogel electrode of the present disclosure, and moreparticularly showing micro-pore size distribution as a function of slitpore width;

FIG. 6 is a graph created using N₂ adsorption measurements of themicro-pores of the carbon aerogel of the present disclosure, showingcumulative micro-pore volume as a function of slit pore width;

FIG. 7 shows a graph of electrosorption of the carbon aerogel of thepresent disclosure illustrating the concentrate collected at differentcharge voltages applied to the cell, for each of ion species NO₃, CI andSO₄; and

FIG. 8 is a graph showing calculated nitrate/chloride andnitrate/sulfate selectivities from the results of FIG. 7.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

The present disclosure relates to FTE-CDI systems and methods whichemploy a new material in a new geometry to further increase the processrate compared to the typical flow between the electrodes of a CDIsystem. The present system and method introduces a FTE-CDI system whichuses a new carbon material (CO₂ activated AARF) for the electrodes ofthe system, described more fully in the following paragraphs, which hasa hierarchical pore size distribution. The hierarchical pore sizedistribution includes a first plurality of sub-nanometer scale pores(“ultramicropores”) to provide adsorption sites, while a secondplurality of pores are included which form micron-sized pores throughwhich water can be pushed at relevant flow rates without requiring asubstantial amount of energy. This material can now be used in adifferent geometry: rather than passing water between the electrodes,the water is pushed through the electrodes. Instead of relying ondiffusion, the salt is actively pushed into and out of the capacitor,which reduces desalination time substantially.

FIG. 1 illustrates one example of an embodiment of flow-throughelectrode capacitive deionization (FTE-CDI) system 100 according to thepresent disclosure. The FTE-CDI system 100 may be viewed as forming asingle “cell” and includes a pair of electrodes 102 and 104, and anelectric circuit 110 that energizes the electrodes 102 and 104. Theelectrode 102 contacts and electrically connects the current collector138, which electrically connects the electrode 102 to one side of theelectric circuit 110, which applies a voltage across the electrode 102.Similarly, the electrode 104 contacts and electrically connects thecurrent collector 140, which electrically connects to the other side ofthe electric circuit 110. The current collectors 138 and 140 may be madeof any suitable metals or metal alloys, but in one preferredimplementation are made from titanium. The current collectors 138 and140 may be foils or wires, and they may be connected to the electrodes102 and 104 using conductive epoxy (e.g., silver epoxy) or paint (e.g.,nickel paint), which is completely sealed or potted in epoxy to preventcorrosion. The electric circuit 110 applies a DC voltage across theelectrodes 102 and 104, which produces an electrical field between theelectrodes 102 and 104.

The electrodes 102 and 104 are arranged such that a flow of the feedwater flows through the electrodes 102 and 104 and in a directionparallel to an electric field applied across the electrodes 102 and 104.While only a single pair of electrodes 102/104 is shown in FIG. 1, inpractice it is anticipated that in commercial applications, the system100 may include two or more pairs of electrodes. Also, it is anticipatedthat a commercial application of the system 100 will likely involveusing a much larger plurality of instances of the system 100, possiblyincorporating hundreds or more such pairs of electrodes 102/104,depending on device size, salt removal, and throughput considerations,and the intended application.

With further reference to FIG. 1, a water-permeable separator 114 madeof an insulative material (e.g., dielectric material) may be disposedbetween the electrodes 102 and 104 to prevent electrical short-circuitsbetween the electrodes 102 and 104. The separator 114 may be made of,e.g., electrolyte permeable paper or a polymer membrane (or polymermembranes). In one implementation the thickness of the separator 114 maybe, for example, less than about 20% of an overall thickness of each ofthe electrodes 102 and 104, and in one specific implementation may be onthe order of no more than about 100 microns thick, and in oneparticularly preferred implementation the separator is about 20-50 μmthick.

Header plates 150 and 152 are disposed to sandwich the electrodes 102and 104 and the separator 114. The header plates 150 and 152 are madeof, e.g., ultraviolet (UV) transparent acrylic material. Alternative toacrylic, other transparent plastic materials may also be used (e.g.,polycarbonate). The header plates 150 provides structural support to theelectrodes 102 and 104 and the separator 114.

An epoxy 154 may be disposed between the header plates 150 and 152 andsurrounding the electrodes 102 and 104 and the separator 114. The epoxy154 may be, e.g., UV-curable epoxy. The header plates 150 and 152 andthe epoxy 154 define a space that accommodates the electrodes 102 and104 and the separator 114. In some embodiments, a combination of theheader plates 150 and 152, the electrodes 102 and 104, the separator114, the current collectors 138 and 140, and the epoxy 154 is referredto as a cell (e.g., an FTE-CDI cell, or a flow through cell). Again, itwill be understood that in a commercial application, a large pluralityof instances of the system 100 (with the system representing one “cell”)is likely to be used.

The FTE-CDI system 100 includes an input flow line 122 and an outputflow line 124. In some embodiments, the input flow line 122 and theoutput flow line 124 are part of the system 100. In some embodiments,the system 100 may include multiple input flow lines and/or multipleoutput flow lines.

The header plate 150 includes one or more flow channels formed therein.For example, as shown in FIG. 1, the header plate 150 is shown toinclude a channel 151, although in practice it will be appreciated thata plurality of flow channels 151 may preferably be formed in the headerplate 150 to distribute a fluid flow evenly through the header plate.The channel 151 of the header plate 150 is in fluidic communication withthe input flow line 122 and the electrode 102. Similarly, the headerplate 152 defines one or more channels 153 therein, and more preferably,a plurality of spaced apart flow channels. The channel 153 of the headerplate 152 is in fluidic communication with the output flow line 124 andthe electrode 104.

Because the space accommodating the electrodes 102 and 104 and theseparator 104 is sealed by the epoxy 154, water can only flow into andout of the cell through the flow lines 122 and 124. Thus, duringoperation, water flow into the FTE-CDI system 100 through the input flowline 122, the channel 151 of the header plate 150 (or multiplechannels), the electrode 102, the separator 114, the electrode 104, thechannel 153 of the header plate 152 (or multiple channels), and theoutput flow line 124.

In operation during a charging stage, as the water flows through theelectrodes 102 and 104, ions from the water are attracted to theelectrodes 102 and 104 and adsorb to the surfaces of the porouselectrodes 102 and 104. During a discharging stage, to avoid ionsaturation on the electrodes 102 and 104, the electrodes 102 and 104 areshort-circuited or applied with a reverse electrical potentialdifference (e.g., by the electric circuit 110). As a result, ionspreviously adsorbed on the electrode surfaces are flushed into wastewater flowing through the electrodes 102 and 104.

Electrode Construction

The electrodes 102 and 104 of the system 100 are new and effectivelywork to capture nitrate molecules from fluids (e.g., water) flowingthrough the electrodes. As shown in highly simplified representativeform in FIG. 1a , each electrode 102 and 104 forms an ultramicroporouselectrode (e.g., carbon aerogel). The terms “ultramicroporous” and“ultramicropores”, as used herein, mean a quantity of pores which areall below, or substantially all below, about 1 nm in width. Theseultramicropores are designated by reference number 102 a in FIG. 1a ,and are distributed randomly throughout each electrode 102 and 104. Inaddition, micron-sized flow paths, indicated by reference number 102 bin FIG. 1a for the electrode 102, are formed with a random distributionthroughout the electrode 102, and extend through the entire crosssection of the electrode 102. With brief reference to FIGS. 4a and 4b ,the micron-sized pores 102 b form a ligament structure throughout thethickness of the electrode 102. The ultramicropores 102 a are present onthe ligaments, so they are essentially uniformly distributed through thethickness of the electrode 102. Electrode 104 may be formed in anidentical manner to also include both the ultramicropores 102 a and themicron-sized pores 102 b. Only the micron-sized pores allow flow throughthe thickness of the electrode 102.

The ultramicropores 102 a of the electrodes 102 and 104 are a highlyimportant feature which enables the system 100 to selectively removenitrate over other ions, especially common divalent species. The reasonfor this is that the ultramicropores 102 a formed in the electrodes102/104 (e.g., carbon aerogel) tend to have slit-shaped pores, as shownin highly simplified form in FIG. 2, and that nitrate is a weaklysolvated disk-like ion (FIGS. 3a and 3b ), making it the perfectlock-and-key situation for selective adsorption (FIG. 2). FIGS. 3a and3b illustrate the nitrate ion, with FIG. 3b illustrating particularlywell the disc-like shape that this ion has. The disc-like shape enablesthe nitrate ion to be easily captured in the slit-shaped ultramicropores102 a. FIGS. 3a 1 and 3 b 2 show graphs which illustrate the projectiondistribution of water oxygens on the planes parallel (FIG. 3a 1) andperpendicular (FIG. 3b 1) to the plane of the anion. In the graphs ofFIGS. 3a 1 and 3 b 1, red=oxygen, white/grey=hydrogen and blue=nitrogen.

The electrodes 102 and 104 were formed in the same manner, and thereforethe following discussion will reference only the forming of theelectrode 102. The flowchart 200 of FIG. 4 summarizes various theoperations used to make the ultramicroporous hierarchical carbon aerogelmonoliths (“pHCAMs”) that are used as the electrodes 102 and 104.Initially at operation 202 a quantity of 430.5 g of resorcinol (3.92mol, 99% Sigma Aldrich) was dissolved in 525.0 g of DI water. Atoperation 204 a quantity of 626.5 g of 37% formaldehyde solution (7.84mol, ACS grade, contains 10% MeOH, Sigma Aldrich) was then added. Atoperation 206 a quantity of 15.4 g of glacial acetic acid (0.245 mol,99+% Sigma Aldrich) was then also added. At operation 208 the reagentswere mixed for 30 min at 40° C. At operation 210 the mixture was thenpoured into a Teflon mold and cured at 23° C. for 46 hours, followed atoperation 212 by aging for 24 hours at 70° C. The aged RF blocks werethen removed from the mold and sliced into thin sheets having athickness of from about 300 μm to about 700 μm, and in one instance athickness of about 500 μm. The sheets were formed by slicing the aged RFblocks with a suitable implement, for example a band saw (e.g., DeltaModel 28-185), as indicated at operation 214. The wet organic aerogelsheets were washed with DI water and subsequently exchanged for acetone,as indicated at operation 216. Wet aerogel sheets were then sandwichedbetween porous silicon carbide sheets, as indicated at operation 218,and then loaded into a custom-made drying chamber equipped with anairflow control unit, as indicated at operation 220. After loading, thedrying chamber was sealed, and the air flow rate set to 80 mL/min, asindicated at operation 222, to dry the aerogel sheets. Dry carbonaerogel were carbonized at about 900° C. to about 1000° C., for about 2to 4 hours, and in one instance at about 950° C. for 3 hours under N₂,as indicated at operation 224, and subsequently activated for about0.5-1.5 hours at a temperature of about 900° C. to about 1000° C., andin one instance for 1 hour at 950° C., with CO₂ flow at 2 L/min in a 6inch tube furnace, as indicated at operation 226. At operation 228 theactivated carbon aerogel was then removed from the furnace and theprocess ends. FIGS. 4a and 4b illustrate high and low magnificationmicrographs, respectively, obtained from a scanning electron microscopeshowing a portion of the ultramicroporous electrode 102 aftercarbonization and activation.

It is important to note that the resulting aerogel is activated to havethe ˜0.3 cm³/g microporosity with pore sizes almost all being below 1 nmin width. FIG. 5 is a graph 300 showing measurements of the micro-poresize distribution from N₂ adsorption measurements of the micro-poresformed in a carbon aerogel electrode of the present disclosure, and moreparticularly showing micro-pore size distribution as a function of slitpore width. FIG. 6 shows a graph 400 illustrating cumulative micro-porearea as a function of slit pore width. It is this micro-pore sizedistribution that is highly important to making the electrodes 102 and104 selective for nitrate. Nitrate, being a planar, weakly solvated ion,is ideal for fitting into the narrow ultramicropores 102 a where otherions either cannot fit or are less energetically stable within. Thispore size distribution is extremely effective in adsorbing nitrate overboth a divalent species and a common interferant ion like chloride.

The electrosorption selectivity of the activated aerogel electrode 102described above was measured in a flow-through electrode CDI cell, theresults of which are shown in FIGS. 7 and 8. To do so, a 3.33 mM/3.33mM/1.67 mM NaCl/NaNO₃/Na₂SO₄ feed solution were used. The CDI cell wascharged at various constant voltages (0.4-1 V) under a constant flowrate (3 ml/min) while monitoring the effluent conductivity. Aftercharging the CDI cell at constant voltage and flow for an extendedperiod of time (>25 min), the CDI cell was discharged to zero volts, andthen the resulting concentrate was collected, stopping once the CDI cellcurrent density decayed to a low value (0.045 mA/cm²). With theconcentrate solution in hand, it was then possible to measure the ionconcentration ratios that were adsorbed onto the electrodes during thecharging phase with ion chromatography. FIG. 7 presents a graph 500illustrating the resulting raw concentration values of nitrate,chloride, and sulfate in the collected concentrate solution. By far, thedominant adsorbed species was nitrate, followed by chloride, and thenlastly by sulfate (NO₃ ⁻>Cl⁻>>SO₄ ²⁻). The sulfate concentrationscarcely deviated from the feed (FIG. 7), indicating that it wasessentially not adsorbed. These results indicate that ultramicroporouscarbon can be used as a highly selective sorbent for nitrate and perhapsother weakly solvated planar ions, even in the presence of divalentions.

FIG. 8 shows a graph 600 which illustrates that the observed nitrateselectivities are exceptionally high when compared to other CDIresearch, especially given that a divalent ion (sulfate) is present inaddition to chloride. Most importantly, these results are obtainedwithout the need for specialized functionalization, membranes, orcoatings. Still further, these results are produced using a relevantmixture with multivalent and chloride interferants. This shows that thecarbon aerogel electrodes 102 and 104 described herein are ideallysuited for selectively removing nitrate from ion mixtures due to anexcellent match between pore structure (narrow slits, mostly below 1 nmin width) and ion solvation properties (i.e., nitrate is a weaklysolvated in the axial direction). The present disclosure also shows thata particular carbon electrode microporosity can be a highly effectiveway to achieve excellent electrosorptive selectivity.

While various embodiments have been described, those skilled in the artwill recognize modifications or variations which might be made withoutdeparting from the present disclosure. The examples illustrate thevarious embodiments and are not intended to limit the presentdisclosure. Therefore, the description and claims should be interpretedliberally with only such limitation as is necessary in view of thepertinent prior art.

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific components, devices, and methods, to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to those skilled in the art that specific details need not beemployed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

When an element or layer is referred to as being “on,” “engaged to,”“connected to,” or “coupled to” another element or layer, it may bedirectly on, engaged, connected or coupled to the other element orlayer, or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” “directly engagedto,” “directly connected to,” or “directly coupled to” another elementor layer, there may be no intervening elements or layers present. Otherwords used to describe the relationship between elements should beinterpreted in a like fashion (e.g., “between” versus “directlybetween,” “adjacent” versus “directly adjacent,” etc.). As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items.

Although the terms first, second, third, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another region,layer or section. Terms such as “first,” “second,” and other numericalterms when used herein do not imply a sequence or order unless clearlyindicated by the context. Thus, a first element, component, region,layer or section discussed below could be termed a second element,component, region, layer or section without departing from the teachingsof the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,”“lower,” “above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. Spatiallyrelative terms may be intended to encompass different orientations ofthe device in use or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the example term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

As used herein, the term “about,” when applied to the value for aparameter of a composition or method of this technology, indicates thatthe calculation or the measurement of the value allows some slightimprecision, resulting (for example) from manufacturing variability,without having a substantial effect on the chemical or physicalattributes of the composition or method. If, for some reason, theimprecision provided by “about” is not otherwise understood in the artwith this ordinary meaning, then “about” as used herein indicates apossible variation of up to 5% in the value.

What is claimed is:
 1. An ultramicroporous electrode for use in a flowthrough, capacitive deionization (FTE-CDI) system for adsorbing nitrateions contained in water being fed into the electrode for treatment, theelectrode comprising: a carbon aerogel member having a hierarchical poresize distribution, the hierarchical pore size distribution including: afirst plurality of ultramicropores each having a shape forming a slit,and substantially all of the first plurality of ultramicropores beingbelow 1 nm in width and forming a slit-like shape; and a secondplurality of pores distributed throughout the thickness of the carbonaerogel member and being sufficiently large to enable fluid flow pathsto be formed through the carbon aerogel member, which enable a flow ofwater to be pushed through the carbon aerogel member; the firstplurality of ultramicropores configured to selectively capture nitrateions carried in the water flowing through the carbon aerogel member; andwherein the first plurality of ultramicropores collectively provide atotal pore volume of approximately 0.3 cm³/g and collectively provide atotal pore area of about 1084 m²/g when the first plurality ofultramicropores are substantially all below 1 nm in width.
 2. Theultramicroporous electrode of claim 1, wherein the first plurality ofultramicropores is distributed throughout the thickness of the carbonaerogel member.
 3. The ultramicroporous electrode of claim 1, whereinthe second plurality of pores each comprise micron-sized pores.
 4. Theultramicroporous electrode of claim 3, wherein the second plurality ofmicron-sized pores are distributed throughout the thickness of thecarbon aerogel member.
 5. The ultramicroporous electrode of claim 4,wherein the second plurality micron-sized pores enable the flow of waterto be pushed through the entire thickness of the carbon aerogel.
 6. Theultramicroporous electrode of claim 1, wherein the first plurality ofultramicropores each form an adsorption site for capturing the nitrateions.
 7. An ultramicroporous electrode for use in a flow through,capacitive deionization (FTE-CDI) system for adsorbing nitrate ionscontained in water being fed into the electrode for treatment, theelectrode comprising: a carbon aerogel member having a hierarchical poresize distribution, the hierarchical pore size distribution including: afirst plurality of ultramicropores each shaped as a slit and each havinga width configured to selectively capture a nitrate ion, and the slitsbeing distributed throughout a thickness of the carbon aerogel member,and each one of the first plurality of ultramicropores having a width ofno more than about 1 nm, and wherein the first plurality ofultramicropores collectively provide a total pore volume of 0.3 cm³/gramand collectively provide a total pore area of 1084 m²/g; and a secondplurality of pores distributed throughout the thickness of the carbonaerogel member, and being sufficiently large to enable fluid flow pathsto be formed through the entire thickness of the carbon aerogel member,which enable a flow of water to be pushed through the thickness of thecarbon aerogel member; and the first plurality of ultramicroporesoperating to form adsorption sites to selectively capture nitrate ionscarried in the water flowing through the carbon aerogel member.
 8. Theultramicroporous electrode of claim 7, wherein the first plurality ofultramicropores are distributed throughout the carbon aerogel member. 9.The ultramicroporous electrode of claim 7, wherein the second pluralityof pores comprise pores on the order of microns in size.
 10. Theultramicroporous electrode of claim 9, wherein the micron-sized poresare distributed throughout the thickness of the carbon aerogel member.